ARCHKAX SANDS

TABLK IV.-.....AUHANOKMHNT or Horns -\M> Il«»« K

Kra or Period, n ' f"

PoHt-TcH'iiary ....
Cainozoic or Tcirtiary

io or Secondary

Novvw J'ulwo/o
or Dt.vutoy.ou'

Oldor Pttliiw/o
or Protortoir

Palaeozoic or
Primary

Kozoic

Permian.

C'nrbunitVrmiH.
Devonian and tMd flni
Siliintm.

I ; Archi'fiti.

AIUIIIBAN SYSTEM,

Archean rocks onjy contain relatively sinsill pn^Mtrti
and such material in usually HO inkTininjjled with <!»«
it must be separated by washing, scnu'iun^j, or otlnT iN*-«
means. Consequently, these rocks an a whole do not i liivrt 1 v

^ «»f f-
r«»**l*

much natural sand. They can only do HO whrn 111
undergone considerable disintegration, us part, of tin* vnuiit*" ««f
Cornwall, Devonshire, and (»ls(jwh(^ro from which <*liinn rlay «»*l
kaolin are obtained, together with considi^rabli* ({uantifii*N of ^aml.
(See China Clay Sands, Chanter III.).
In addition to the small particles conntitutinK Mieh |*nn*.piry
sands there are various ignooun rocks, inehtdini/ |«'tffiwtit«'H,
aplites, microgranites, and modified granites, which may b»* y.r«Miii*l
and so used as sources of sand which is very suit-able for ?*«nw
purposes when the rocks are sufficiently free.! from iron cnuipcunfl*
and other undesirable impurities. The cost of crushing is, how-
ever, in many cases prohibitive and the*, igneous roekn IMMUJ.' «»f ;t
complex character— seldom produce Hands of high quality. Sum**
rocks which contain clastic felspar may, when eruHhi'd, b- of valur
for glass-making, as, for example, granophyre from hrnudy l*iil,
Climber land.
The portions of igneous rocks c.omponed of almost pun* quart/*
are, unfortunately, generally UHC^CSH on a<?count of the great ro*t
of grinding, sifting, and washing them. For many pur] HIM** al»»i»
the crushed rock is not so suitable an the incoherent naml, MO flint ,
except in rare cases, crushed quartz is of very limited apptiratioit.